Craftsman's Mark hidden on the Cal. 6870 of the Seiko Credor U.T.D line
The Cal. 6870 is a groundbreaking caliber emerged as one of the thinnest movements of its time, opening new opportunities for the creation of ultra-thin dress watches for Seiko Credor.
This technical masterpiece found its home in Seiko's prestigious U.T.D. (Ultra Thin Dress) line, where it demonstrated the perfect marriage of engineering ingenuity and aesthetic refinement. The movement's exceptional thinness allowed watchmakers to craft timepieces with remarkably slim profiles, challenging the conventional limitations of watch design.
Cal. 6870A next to a Japanese 1 Yen
Grail Watch Reference has an extensive article of the Cal.68 family: https://reference.grail-watch.com/movement/seiko-6830/
For enthusiasts who owns a Credor equipped with the Cal. 6870, the sapphire crystal case back offers a window into this movement. The movement's finishing reflects attention to detail, featuring several distinctive elements:
- The Credor crown logo (with and without "Seiko")
- The movement reference
- The jewel count
- A "Japan" inscription
Sometimes, additional information appears on the movement. For example, the GZAQ997 and GZAQ995 models, exclusively sold at the Shizukuishi Studio, have extra engraving. These models feature "Shizukuishi Studio" written in Kanji ("雫石高級時計工房") on the movement.
These small details and variations from the standard movement design are particularly exciting for us watch enthusiasts.
Cal. 6870A bearing the engraving of 雫石高級時計工房
Mark of a Master Craftsman - Mamoru Sakurada 桜田守, 1 of the 3 founders of Shizukuishi Watch Studio
In the old days of craftsmanship, artisans have long left their mark on their creations—a practice that speaks to both pride and accountability. While this tradition continues among independent watchmakers, it remains exceptionally rare for established manufacturers like Seiko to acknowledge individual watchmakers through such personal signatures.
The story of Shizukuishi Watch Studio, a name that resonates deeply with Grand Seiko aficionados, begins in 2004 under the guidance of three master watchmakers: Akira Oohira, Mamoru Sakurada 桜田守, and Kiyoshi Terui 照井清. This prestigious studio would become the birthplace of numerous horological achievements, from the highly precise 9S movements to the exquisitely crafted Credor ultra-thin timepieces.
Mamoru Sakurada & Cal. 6870
Among them, Mamoru Sakurada led the development of the Caliber 6870 movement that enabled the relaunch of Seiko's iconic Ultra Thin Dress (U.T.D.) watch line. By creating one of the thinnest movements of its time, Sakurada elevated the overall level of craftsmanship at Shizukuishi and Seiko as a whole.
As the lead developer of the 6870 movement, it's plausible that Sakurada san personally assembled many of these movements. However, it's worth noting that while this is a reasonable assumption, we can't be certain without specific information about Seiko's production processes at that time.
Leave a legacy, make a mark
Perhaps the most intriguing aspect of Sakurada's legacy appears on the U.T.D. 120th Anniversary Limited Edition GBAQ987 model. While no official documentation explicates this engraving, many enthusiasts interpret it as either a shield or heart motif. However, I believe this subtle marking pays homage to Sakurada himself, ingeniously combining select components from the three kanji characters (木, 田, and 寸) that make up his name (桜田守) into an artistic personal signature.
Red arrow indicating the Sakurada's craftsman mark:
Credor GBAQ987 UTD 120th anniversary limited edition of 100 bearing an alleged Sakurada-San's Craftman's Mark
The GBAQ987's accompanying documentation pays tribute to Sakurada's achievements, featuring a page dedicated to his career milestones. At the bottom, his signature—桜田守—appears in a distinctive calligraphic style, with all three kanji characters flowing together in one unbroken stroke.
GBAQ987 - Booklet depicting Mamoru Sakurada as the watch maker behind this model and his signature
The Rarest of Marks - GZAQ991
In addition to the GBAQ987, I have only come across one other example displaying Sakurada Mamoru's craftsman's mark: the GZAQ991. Released in 2011 to commemorate the World Watch Fair at Tokyo's Nihonbashi Mitsukoshi department store, this exclusive creation was limited to just seven pieces. The watch features Sakurada's distinctive "shield" marking beneath the Credor logo, and his signature on the movement mirrors the one found in the GBAQ987's documentation.
These rare timepieces, bearing the personal mark of a master craftsman, stand as enduring testimonials to Sakurada's illustrious career and his profound influence on Japanese watchmaking. They represent not just technical excellence, but the preservation of a craft tradition that continues to inspire collectors and enthusiasts alike.
Sakurada Mamoru's craftsman mark and his signature on GZAQ991
Close up of 6870a movement on my GZAQ991
Strap of choice for my Credor: Togo Zaffre Blue
